P2A39: O2 Sensor Positive Current Control Circuit Low Bank 1 Sensor 3

P2A39 is set when the pump-current lead feeding the rearmost wide-band probe on bank 1 (sensor 3) is pulled below its permitted window, typically because the wire rubs through to chassis ground near the hot rear exhaust section. At ignition-on Saab's 2010 9-5 shows roughly 2.8 V on the pump-current pins of its front probe, so a reading near zero points to a ground short. No manufacturer publishes P2A39 itself; Ford stores a short to ground on the IP wire of its front probes under P0131, and CARB only requires that such out-of-range signals be caught. P2A38 covers the open line, P2A3A the high side, P22AC the sensor 2 case. Apart from the warning lamp, the aftertreatment monitors using this probe stay incomplete.

Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.

Symptoms

• Check engine light after repeated detection
• Sensor 3 reading implausible or missing in live data

Most likely causes

• Pump-current wire chafed through to body or exhaust bracket
• Internal short in the probe after thermal shock or water ingress
• Faulty sensor interface in the engine control module

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the wiring and connector of the sensor indicated
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Look for exhaust leaks
4. Check the signal in live data with the engine warm
5. Check the fuse and the heater resistance if the code mentions it
6. Replace the sensor if it has power and does not respond

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P2A39 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• A: Hybrid or air and fuel
• 39: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2A39?

Yes, you can normally drive in moderation, but get it repaired soon: you will use more fuel and the catalytic converter can be damaged over time.

What causes code P2A39?

The most common causes are: pump-current wire chafed through to body or exhaust bracket; internal short in the probe after thermal shock or water ingress; faulty sensor interface in the engine control module.

Related codes

• P2A38O2 Sensor Positive Current Control Circuit/Open Bank 1 Sensor 3
• P2A3AO2 Sensor Positive Current Control Circuit High Bank 1 Sensor 3
• P2A3CO2 Sensor Negative Current Control Circuit Low Bank 1 Sensor 3
• P22ACO2 Sensor Positive Current Control Circuit Low (Bank 1 Sensor 2)
• P0143O2 Sensor Circuit Low Voltage Bank 1 Sensor 3

Sources

• saabwisonline.com: dtc p2237 p2239 p2243 p2251 or p2626
• newtonnet.co.uk: fordobd2012
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.